With advances in electronic products, semiconductor technology has been applied widely in manufacturing memories, central processing units (CPUs), liquid crystal displays (LCDs), light emitting diodes (LEDs), laser diodes and other devices or chip sets. In order to achieve high-integration and high-speed requirements, dimensions of semiconductor integrated circuits have been reduced and various materials, such as copper and ultra low-k dielectrics, have been proposed and are being used along with techniques for overcoming manufacturing obstacles associated with these materials and requirements. When scales of integrated circuits are reduced, thickness variations of layers of the integrated circuits may affect electrical performance thereof.
FIG. 1 is a cross-sectional view of a traditional nitride removing bench. Referring to FIG. 1, a nitride removing bench 100 includes an inner tank 110 next to an outer tank 120. The inner tank 110 accommodates phosphoric acid 115 for removing silicon nitride from substrates (not shown). The phosphoric acid 115 overflows into the outer tank 120. A cycling system 130 is configured to cycle phosphoric acid 125 stored in the outer tank 120 to the inner tank 110 through a tube 131. The cycling system 130 also has a pump 133, a heater 135 and a filter 137 connected in series. A refreshing system 140 includes a tube 141, providing fresh phosphoric acid 145 at or near to the top surface of the phosphoric acid 125. An overflow system 150 including a tube 151 is configured to remove the excess of the phosphoric acid 125 from the outer tank 120.